Remove .github/{ISSUE,PULL_REQUEST}_TEMPLATE

The files were not really templates but instructions. These instructions
are already spelled-out in CONTRIBUTING.md and repeating them feels a
bit redundant.

If it turns out people don't read CONTRIBUTING.md when submitting issues
and pull requests, I'll probably restore the templates (likely in some
shorter/simpler form).

.github/ISSUE_TEMPLATE.md

@@ -1,20 +0,0 @@
-Checklist:
-
-  * [ ] This is not a question (these belong to the [Google Group][google-group])
-  * [ ] I searched existing issues to make sure I don’t create a duplicate one
-
-For bug reports, please include:
-
-  * Steps to reproduce
-  * What I expected to happen
-  * What happened instead
-
-In most cases, it is also useful to include a **minimal** example (grammar + input)
-reproducing the problem.
-
-For feature requests, please include:
-
-  * Feature description
-  * Why do you request it
-
-[google-group]: https://groups.google.com/forum/#!forum/pegjs

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,11 +0,0 @@
-Checklist:
-
-  * [ ] The change is trivial (if not, I filed an issue first)
-  * [ ] The change is split into atomic commits
-  * [ ] Commits have messages adhering to [these conventions][git-commit-messages]
-  * [ ] The change is documented (if needed)
-  * [ ] The change is tested (if needed)
-  * [ ] The change passes the specs (`make spec`)
-  * [ ] The change passes ESLint checks (`make lint`)
-
-[git-commit-messages]: http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html